This application claims the priority of German Application No. 29908347.0, filed May 10, 1999, the disclosure of which is expressly incorporated by reference herein.
1. Field of the Invention
The invention relates to electromagnetic (EMC) shielding of walls or parts of a casing or housing, particularly a table casing or housing, which has side parts, transverse sections, a cover plate and a base plate, in which at least the cover plate is provided with lateral marginal legs in the vicinity of the side parts and marginal legs in the vicinity of the transverse sections.
2. Discussion of the Background
German Patent document DE 295 02 404UI discloses an EMC-shielded means with two front and two rear transverse sections between two side parts. A cover plate and a base plate are fixed to the side parts with the aid of plug connections. Finger-like engagement elements are provided as plug connections particularly on the side parts. These elements cooperate with receptacles constructed in a complementary manner, e.g. approximately trapezoidal bulges, particularly in angular marginal legs of the cover plate and the base plate. Contact studs are constructed in the area of the plug connections as EMC shields and when the finger-like engagement elements are inserted in the receptacles, material abrasion and contacting occurs.
In conventional devices the front and rear transverse sections are integrated into the base and cover plates. There is an EMC shielding at the front by EMC spring contact strips, which are positioned on angular legs of the front panels.
It is known to provide such subassembly carriers with an external housing or casing for use as a table housing.
The object of the invention is to create a structure for EMC shielding of a housing, particularly the side parts and transverse sections with respect to a cover plate and/or base plate, which ensures an extremely simple construction, a rational manufacture and a particularly efficient EMC shielding.
According to the invention this object is achieved by a housing, which has side parts and transverse sections, as well as a cover plate and a base plate. At least the cover plate is provided with lateral marginal legs in the vicinity of the side parts and marginal legs in the in the vicinity of the transverse sections, wherein the side parts, at least on their upper edges, are provided with labyrinth-like areas. The labyrinth-like edge area are formed by at least two supports for the cover plate and/or base plate. The lateral marginal legs of the cover plate and/or base plate extend over and beyond the labyrinth-like edge areas and are preferably oriented parallel to the side parts.
The fundamental ideal of the invention is an EMC shielding concept, which is based on labyrinth-like areas of the side parts, the cover plate and/or the base plate.
According to the invention, in their upper and/or lower edge areas and appropriately over their entire depth, the side parts are so bent or bevelled that a fitted cover plate and/or base plate rests or engages thereon with at least two supports.
According to an advantageous construction the bevels of the side parts are constructed as a labyrinth bow. High shielding efficiency values occur with a labyrinth-like edge area, which in cross-section is constructed roughly as a horizontal Z or as a U or V-shaped groove.
According to the invention, the lateral marginal legs of the cover plate and/or base plate in each case extend over the labyrinth-like edge areas, so that the latter are covered. The lateral marginal legs are generally 90xc2x0 bends and are parallel to the side parts.
It is particularly advantageous for the length of the lateral marginal legs of the cover plate and/or base plate to be such that at very high frequencies they have approximately a xcex/4 character. Electromagnetic waves entering the U or V-groove are attenuated to a surprisingly high degree, particularly by reflection and absorption.
The labyrinth-like edge areas and at least the supports together with the corresponding bearing areas of the cover plate and/or base plate, are kept free from paint finishes, so that a metallic contact face is present. When constructing a U or V-shaped groove with an inside connecting leg and an outside free leg, it is advantageous for an outside support to be located on the free leg in a corner area of a fitted cover plate.
A further intermediate space with the side parts is formed by the lateral marginal legs of a cover plate or base plate running parallel to the side parts in the case of a corresponding marginal leg length. It is also possible to lengthen the lateral marginal legs with additional wall elements. Electromagnetic waves entering the intermediate space between the lateral marginal legs or extended lateral marginal legs are also attenuated by reflection and absorption.
It is particularly advantageous that the labyrinth-like edge areas are suitable for receiving an additional EMC seal. For example, an EMC sealing strand can be inserted or fitted in the U or V-shaped groove of the labyrinth-like edge areas, so that the transfer resistance between the cover or base plate and the side parts are further reduced and EMC shielding is improved.
According to a further development of the EMC shielding concept according to the invention, there is also a labyrinth-like construction in the region of the transverse sections, particularly the front transverse sections, with respect to the cover plate and/or base plate and also with this EMC-shielded means there can additionally be provided a seal for increasing the shielding action.
In the vicinity of the transverse sections, the cover plate and/or base plate has, in each case, a double-walled edge area, which is terminally provided with a marginal leg. This marginal leg is vertically oriented and engages in a groove of the transverse section, which is appropriately constructed in slot-like manner in an area directed towards the housing interior.
The double-walled edge area comprises a bearing leg, which is parallel to the actual cover or base plate, and, in the fitted state, rests on the transverse section of the housing. It is particularly advantageous if the bearing leg and transverse section are dimensioned in such a way that the transverse section is virtually covered. A front leg between the bearing leg and the actual cover or base plate is rearwardly inclined, so that the edge area has a roof-like construction. The double-walled edge area can, in cross-sections, also be locked upon as a slightly displaced, horizontal U.
The groove in the transverse section is constructed in complementary manner to the terminal marginal leg of the cover and/or base plate. The marginal leg also passes over the entire width of the transverse section or the housing and is so designed that it is almost completely embedded in the transverse section groove. As a result of the design as a labyrinth, high shielding efficiency values are obtained.
When an EMC seal is also provided, it is appropriate to provide the transverse section with a fastening web, which internally bounds the slot-like groove and serves to receive an EMC spring contact strip. Stud or point contacts on a spring section, which are directed into the groove when the EMC spring contact strip is sealed on, ensure an effective contacting of the marginal legs and also high shielding efficiency values.